Title: Systematic analysis of cell death regulation in mosquitoes. Cell death (apoptosis) is an important component of the vector/host immuno-response mechanism. It has been implicated in the infectious life cycle of a variety of pathogens, such as the malaria parasite and the West Nile virus, in mosquitoes. However, our understanding of cell death regulation in mosquitoes has been hindered greatly by the lacking of a complete list of major insect cell death regulators, i.e. the *Reaper/Hid/Grim -like IAP-antagonists, in the annotated mosquito genomes. IAPs (Inhibitor of Apoptosis Proteins) are the essential [unreadable]Brake[unreadable] of the core cell death machinery in insects. They bind to caspases and inhibit the activity of these [unreadable]deadly[unreadable] enzymes. Genetic studies in Drosophila have shown that most programmed cell death during development is mediated through specific expression of IAP-antagonists such as reaper, hid, and grim (RHG) in cells destined to die. Most of these IAP-antagonists are also required for mediating cell death in response to environmental stress. The genome project for the primary malaria vector, Anopheles gambiae, revealed a significant expansion of the IAP and caspase gene families when compared to Drosophila. This was postulated to reflect the functional requirement of fine-tuning cell death regulation in response to parasite and virus infection. It also strongly implies that the IAP-antagonist ?? IAP ?? Caspases pathway, as is in Drosophila, is fundamentally important for cell death regulation in mosquitoes. However, due to extensive sequence divergence, the annotated complete An. gambiae genome sequence did not initially include any ortholog of RHG-like IAP-antagonist. Using a systematic bioinformatics approach, we identified and subsequently characterized the first RHG-like IAPantagonists, michelob_x (mx), in Anopheles and Aedes genomes. To probe the involvement of these pro-apoptotic genes in mediating vector-pathogen interaction, we identified the mx ortholog in Culex and found that it is induced by CuniNPV (a mosquito baculovirus) infection to Cx.quinauifasciatus (section 4.5;Zhou et al, in preparation). In addition, we have identified another IAP-antagonist, IBMP6, as the ortholog of Drosophila Hid. Interestingly, ibmp6 is induced by MIV infection of the Aag2 cells (section 4.6). These data indicate that like in Drosophila, multiple IAP-antagonist are required for cell death regulation in mosquito. Further more, distinct IAP-antagonists is(are) utilized against different infections or in different tissues. Since the IAP-antagonist genes play pivotal roles in insect cell death regulation and our work revealed that they are involved in pathogen-induced vector response, elucidating fully this group of genes in mosquitoes will be essential for the comprehensive understanding of cell death regulation in response to pathogen challenge as well as during normal mosquito life cycle. This proposed project aims at (1) Systematic identification and functional verification of the IAP-antagonists in major mosquito genomes. (2)Elucidating the role of these IAP-antagonists in mediating vector-pathogen interaction using CuniNPV, MIV, and B.algerae. (3) Developing public resources for systematic analysis of cell death regulation in mosquitoes. Cell death (apoptosis) is implicated in the infectious life cycle of a variety of pathogens, such as the malaria parasite and the West Nile virus, in mosquitoes. Understanding cell death response will help us to develop strategy for controlling mosquito transmitted disease and for controlling mosquito population.